In such devices the designer has a choice as to the amount of functionality carried in the syringe assembly and that in the reusable part of autoinjector. Generally greater functionality in the syringe assembly increases the complexity and/or component count although other factors are important such as safety, comfort and ease of use. Where, as is often the case, a reusable device has no internal power source for the drive mechanism, the drive mechanism must be primed or charged during an arming operation. In a known type of reusable device such as disclosed in EP0666084 there is a direct 1:1 relationship between the force to prime the spring and the force delivered by the spring. This means that the user has to input same magnitude of force into the device to arm it. This can be problematic because if quite a strong force is required it may be beyond what the user can easily apply safely without slipping. But of equal if not greater significance is that, particularly for apprehensive users, an arming process which requires application of a strong force may suggest a powerful or fierce injection operation. There is therefore a need for an autoinjector in which a soft arming force is effective.